1. Field of the Invention
The present invention relates to low temperature sintered ceramic wiring boards and a method for their manufacture. In particular, the present invention relates to low temperature sintered glass ceramic wiring boards in which a low melting point metal such as Ag, Pd or Au, or a mixture of such a low melting point metal and Pt is metalized as a wiring material.
2. Related Art
Wiring boards employing an alumina-based ceramic as an insulating material are used as wiring boards for the mounting of semiconductor elements such as LSIs. However, since the sintering temperature of such an alumina-based ceramic material is high, there are the following problems. Since a high melting point metal such as W or Mo is used as a wiring material that can be sintered at the same time, the electrical resistance of the wiring layer can be as high as 10 to 20 m.OMEGA./mm.sup.2. Thus, wiring boards have been in which a low resistance wiring material, such as Ag or Au, and a low temperature sintering insulating material, such as glass or glass ceramic, could be sintered at the same time. In particular, glass ceramic wiring boards can be sintered at a low temperature of about 800 to 1100.degree. C. and also have excellent mechanical strength since they contain a ceramic crystal phase as a structural component. Therefore, such glass ceramic wiring boards have received much attention recently.
However, the metalization composition used for such wiring boards is made of Ag or Au and optionally include Pd, Pt, or the like, so that its sintering commencement temperature is about 600 to 700.degree. C. On the other hand, the glass ceramic has a softening point of about 700 to 900.degree. C. When there is a large difference between the commencement temperature of the metalization composition and the sintering commencement temperature of the glass ceramic, during the initial stage of sintering only the metalization composition starts to compact and the glass ceramic starts to compact at a higher temperature; thus, a difference in compaction exists. As a result, the wiring board is warped or deformed and it becomes impossible to obtain a board of the prescribed dimensions and shape. As a countermeasure, there has been considered a method in which a glass component having a softening point similar to or higher than that of the glass ceramic is added to the metalization composition, but the sintering commencement temperature of the metalization composition is not greatly increased. There is another method in which a ceramic substrate of alumina, for example, having a flat surface is placed on the wiring board during sintering to forcibly suppress warping. However, when the size of the wiring board increases, there arise problems that uniform compaction cannot be achieved and that the wiring board becomes stuck to the ceramic substrate.